For use in super computers and fast data networks in the context of information technology, there are under development integrated circuits as fast microwave components. Of greater significance are integrated circuits on GaAs chips. Components which have been used hitherto in this context are the MESFET and the HEMT. They both are so-called field effect transistors (FET), in which the current transport is parallel to the surface of the chip. An important speed determining parameter, the so-called "transit time under the gate" is here limited by the smallest lateral structuring of the gate achievable lithographically.
The permeable base transistor (PBT) proposed already in 1979, also deals with the principle of a field effect transistor, although with a current flow direction perpendicular to the chip surface, in which the "transit time under the gate" was significantly reduced.
This had its basis in that the gate length in the vertical structuring was given by the thickness of the epitactically deposited base layer. With the methods of modern epitaxy, like modular beam epitaxy (MBE), metal organic gas phase epitaxy (MOCVD) or metal organic molecular beam epitaxy (MOMBE, CBE, GSMBE) for production of the metallic structured base, layer thicknesses in the range of several atom layers can be produced in a controlled manner.
German Patent Application DE 40 25 269.8 describes a permeable base transistor of GaAs. Several layers are bonded with one another to form the active elements of the components, namely, emitter, base and collector. The lateral finger-like structured base forms at its boundary surface a pn transition with the material surrounding it. These components as a result of this characteristic have also been designated as permeable junction base transistors (PJBT). The thus formed space charge zone is controllable via the highly doped conductive base. The basic material for the region surrounding the base and to which the current channels between the fingers of the base belong, is GaAs with an n-doping in the range of 10.sup.17 to 10.sup.18 cm.sup.-3. The p-doping of the base in the range of 10.sup.20 to 10.sup.21 cm.sup.-3 is achieved with the aid of a carbon doping.
The space charge zones formed on the boundary surface of the base are used for control of the electric current in the region of the current channels with the aid of a suitable voltage bias on the base. In this case it is a disadvantage that in the remaining space charge zone in the region of the lateral boundary surface of the base layer and spreading out therefrom, there is a parasitic space charge capacitance which limits the switching speed of the component disadvantageously.